Let's not turn this into a EU vs NA thing again. We all know North Americans like their conferences and playoffs while Euros like their WCL style seasons. And that's fine. Both systems have their merits and drawbacks for MK8 in particular, though.
Essentially, the NA system is trying to get the maximum out of any current season, favoring exciting individual matches and results over fairness and consistency, making it the ultimate goal for teams to have a shot at winning the whole thing for as long as possible. The EU system has more focus on fairness, but it inevitably loses a lot of the possible rewards for teams in that very season. Instead, the rewards are connected to the upcoming season, because your previous placement will affect which competitions you get to participate in the following season. Take soccer for instance, where like the top 2 teams get to play in the Champions League, 3rd and 4th get to play qualifiers for the CL, 5th and 6th get to play Euroleague, 7th gets to play qualifiers for the EL, etc. And then of course you have a working relegation system, something completely absent from the NFL and the like for instance.
That said, most of the benefits of the American system can be applied to MK8 league as well, such as the excitement about the playoffs, upset wins, etc. However, the reward system of the EU system really doesn't work very well with MK8. There are no KO-tournaments with huge prize pools that you can qualify for by getting say 3rd in a 6-team division. In a community where teams are fluctuating so heavily during and between seasons it's just not serviceable to try and pay out the rewards for a season in the season after, because so much could change by then. We do have sort of a relegation system, but it's really more of a general seeding system that merely uses last season's placement as one factor to determine the seedings of teams.
Personally, I'll always take fairness over anything else and I much prefer the EU league structures over the American system (except I love the draft system, though that doesn't actually affect the season structure itself). But objectively the NA system fits MK8 more.
Despite that, I'll still prefer WCL style over anything else as long as the latter forces me to play more than one match per weekend, though that's a different topic and it doesn't really have anything to do with the league structure as such, so don't mind me on that one.